Antennas



` May 5, 1959 L. D. BALDWIN ANTENNAS 3 Sheets-Sheet 1 Filed Jan. 23,1957 /llllllllllll/I.

INVENTOR LEROY D. BALDWIIN ATTORNEY l.. D. BALDWIN LER INVENTOR. OY D.BALDWIN ATTORNEY VSWR May 5, 1959 L. D. BALDWIN 2,885,676

ANTENNAS TTTTTT EY United States Patent D ANTENNAS Lero,v D. Baldwin,Rochester, N.Y., assignor to General Dynamics Corporation, Rochester,N.Y., a corporation of Delaware Application January 23, 1957, Serial No.635,669

8 Claims. (Cl. 343-767) This invention relates to antennas and isparticularlyl directed to antennas for directionally radiating or receivSuch antenna structures are adapted for mounting in the hull of a shipor aircraft with the cavity structure inside the hull and the slotopening covered with an electrical transparent sheet of insulatingmaterial ush with the hull.

At the high frequencies, such as 1000 to 10,000 megacycles, thedimensions of the probe and of the cavity become so small, and themanufacturing tolerance so critical for a given radiationcharacteristic, as to render the unusual slot antenna structure costlyand unfeasible in manufacture. The probe size and shape especiallyshould be easily reproduced, and at these high frequencies the saidtransmission line should be without discontinuities and free of spuriousradiations throughout the length of the transmission line.

The object of this invention is to provide an improved y slot typeantenna structure.

A more specific object of this invention isto provide an antennastructure adapted for microwave energy that is inexpensive and easilyreproduced in manufacture.

A still more specific object for this invention is to provide amicrowave antenna which is directional and which easily radiates orreceives microwave signals over a wide band of frequencies.

The objectives of this invention are attained by utilizing printedcircuit structures comprising a sheet of insulating material of lowhigh-frequency loss characteristics. To one side of t'ne sheet isprinted an antenna feed transmission line conductor terminating in aprinted flat probe of the desired size and shape. To the other side ofthe sheet is adhered a conductive sheet of metal called a ground plateand of extended area compared to 'the area of the probe and itstransmission line. A window is cut or otherwise formed in the groundplate opposite the probe. A cavity housing is placed over the window,the

lhousing being of measured size and shape to eiiiciently radiate thehigh frequency energy from the probe outwardly through the window.

Other objects and features of this invention will become apparent tothose skilled in the art by referring to the specific embodiments of theinvention discussed in the following specification and shown in theaccompanying drawing in which Figure l is a plan view of one antennastructure em bodying this invention, s

Figure 2 is a section on line 2 2 of Figure 1,

Figure 3 is a plan view of another antenna structure embodying thisinvention,

Figure 4 is a section on line 4 4 of Figure 3,

Figures 5 and 6 are plan and sectional views, respectively, of stillanother structure embodying this invention,

l 2,885,676 Fatented May 5, 1959 "lee Figure 7 is a graph of the voltagestanding Wave ratio versus frequency of one specific probeconfiguration, and

Figure 8 is a polar diagram of the radiation fields of one antennastructure of this invention.

Referring to Figure 1, the antenna of this invention comprises the sheet1 of insulating material, the sheet being relatively thin and havinggood high-frequency insulating characteristics. The sheet may comprise,for example, Tellen-impregnated fibre glass. In the preferredembodiment, the underside of the sheet is covered, overall, with a thinfoil or plate 2 of copper or other electric conducting metal, preferablyglued firmly to the insulating sheet. To the other side of sheet one isformed the;l transmission line 3 terminating in the probe 4. The liueandprobe, according to this invention, are printed on the sheet 1. Whilevarious printing techniques may be used,A the one which has been foundto be easily controlled in manufacture consists of laminating the sheet1 with thin copper foil-sheets on both sides by any pressure-heattechnique which will firmly bond the laminae together. The copperlaminate on one side is then smeared with a thin layer of photo-resitvarnish, whereupon the varnish is irradiated with a strong light whichwill chemically fix the varnish, the irradiation being done through anegative of the printed circuit pattern desired on the copper sheet. Inthis case, the negative pattern would have the precise outline anddimensions of the transmission line 3 and probe 4. After Washing awaythe unfxed portion of the varnish, the exposed copper plate is thenetched away in a suitable etching solution to leave only the metal inthe outline of 3 4, Figure l.

According to an important feature of this inventiona "window 5 isremoved from the ground plate 2 opposite the probe 4 either by cuttingaway the metal or by the etching technique above mentioned. The window 5and probe 4 are so positionally related that the probe overlies thewindow, preferably but not necessarily, at the center of the window.

-It has been found that where the conductor 3 is spaced from the groundplate 2 by a fraction of the width of the conductor and where the highfrequency insulating properties of the sheet are good, radiation fromthe transmission line is negligible. The thickness of the insulatingsheet and the width of the conductor 3 is easily controlled within verynarrow tolerance limits, which means that the impedance characteristicsof the transmis- `sion line 2 3 are easily controlled in manufacture.Be-

cause the parts of the transmission line, probe, and ground plate arebonded together, relative movement of the parts is not possible in use.

While the window 5 in Figure 1 is shown rectangular in shape, the windowmay be round, oval, or other shapes depending in part on the directionalcharacteristics of the antenna desired. The ground plate, according tothis invention is joined to the housing 6 as by flanges 7 which can besoldered or otherwise aixed to the ground plate 2. The size and shape ofthe housing 6 is chosen to enclose completely the window. The cavitywalls may be set flush with the edge of the window o1' outwardly fromthe edge, depending on the electrical and space requirements of thecavity. In the example shown in Figure 2, the depth of the cavity formedby the housing is adjustable by the plungeriS carried on the adjustingscrew 9. The plunger 8 forms an imperforate barrier to the field withinthe cavity and yet slideably engages the Walls of the housing. Springfingers 8a on the plunger slide on the wall. The distance from the probe4 to the face of the plunger 8 may be made proportional to any smallfraction of the wave to be radiated, depending on the mode of cavityoperation desired. Where broad band operation is desired, the depth ofthe cavity may be one quarter wavelength. tOdd numbered quarterwavelengths may be 3 used, .but the Ahigher the `number the narrowerbecomes the band.

The printed circuit board 1-2-3 with the mounted cavity 6-7-8 may thenbe mounted, as shown in Figure 2, directly on the metal chassis 10 fromor to whichmicrowave energy can be radiated. It will be noted with theground plate 2 in contact with the wall 10 of the chassis, the groundplane is electrically extended to the limits of the chassis.Alternatively, of course, the cavity structure 6 with anges 7 could bemechanically mounted on the chassis wall, rather than on the groundplate 2 as shown.

The printed circuit board of Figure 2 may be turned over as shown inFigures 3 and 4. Such a reversal places the ground plate to the outsideand opposite the cavity housing 6a, and the transmission line and probe3, 4 adjacent the housing. In such a structure the housing 6a is cutoutor relieved at 6b to clear ,the transmission line 3. Bolts 11 throughanges on the cavity housing and through the ground plate effectivelyground the housing lto the plate.

It has been found convenient on occasion to space the printed circuitboard 1 inside the chassis housing 10, as shown in Figures and 6. Awindow `5a of measured size and shape is formed in the chassis housingin alignment with the window 5 of the ground plate 2. The spacing collar12 is clamped between the two plates 1 and to electrically continue thecavity of housing 6a to the periphery of Window 5a, and to rigidlymechanically x the parts of the antenna structure together. It willappear that the spacing collar 12 must be provided with a small notch orcutout 12a to clear the transmission line 3. Various circuits kdesignedfor microwave operation are conveniently placed in the narrow `spacingbetween the two plates 1 and 10, and are effectively shielded fromequipments that may be mounted on the base plate-side of the sheet 1.

The voltage standing wave ratio of one antenna of this invention isshown in Figure 7, the specilic dimensions of the cavity and of theprobe, being shown in the figure. It will be noted that the voltagestanding wave ratio is relatively low and uniform from about 340() to8000 megacycles. It was found that when the area of the printed probeand its cavity were made larger, lower frequency characteristics weredisplayed. The radiation pattern in the horizontal and elevationalplanes are quite symmetrical about the medium line of the window asshown in Figure 8. In Figure 8, the radiation pattern in the H plane for5000 megacycles is plotted by a solid line, and in the E plane radiationis plotted by a dashed line. The symmetry of the patterns about themedium line of the antenna window is attributed to the controllabledimensions and spacings of the printed probe on the board 1.Occasionally, a small spurious lobe is experienced.

Many modifications may be made in the specific structures herewithdisclosed Without departing from the spirit of the invention as definedin the following claims.

What is claimed is:

l. An antenna assembly comprising an imperforate self supporting sheetof insulating material, said material having low high-frequency losscharacteristics, a ground plate of extended area adhered to one side ofsaid sheet., a window in said ground plate to ,expose .said sheetthrough the window, a metal box with one open side placed over thewindow and electrically joined substantially throughout the rim of theopen side of said box to said plate to create a closed cavity .open onlythrough the window of said insulating sheet; and a printed conductor onthe other side of said sheet vterminating in Asaid window.

2. A slot antenna for microwaves comprising a printed circuit board,said board being a sheet of insulating material with an antenna probe ofpredetermined size and shape, and a lead-in conductor to the probe,outlined by metallic plating bonded directly to one side of said sheet;a ground plate bonded directly to the other side of said sheetunderlying said lead-in conductor, said plate having a cut-out windowopposite said probe; and a rigid sheet-metal cavity housing over saidwindow and electrically and mechanically connected to said plate.

3. A unitary antenna assembly comprising a stiff selfsupporting sheet ofinsulating material, a ground plate adhered directly to one Asurface tosaid sheet, said plate being of extended area and having an openingtherethrough; a printed transmission line bonded on the other surface ofsaid sheet terminating opposite said window, and a housing overlyingsaid window and joined mechanically to said sheet and connectedelectrically to said plate throughout the periphery of .said window,said housing being closed on all sides and having predetermined internaldimensions so as to funciton as a microwave cavity at lthe operatingfrequencies.

4. A slot microwave antenna combination comprising an extended sheet ofinsulating material of good high frequency characteristics, a groundplate laminated to one side of said sheet, said plate having a window ofmeasured .size and shape; and a concaved metal housing with one openside, the opened side of said housing being placed over said window andthe edges of the housing around the open side being connectedelectrically and mechanically to said ground plate.

-5. An antenna assembly comprising a sheet of insulating material, aground plate adhered to one side of said sheet and a transmission lineadhered to the other side vot said sheet, a -window in said groundplate, said transmission line terminating opposite said window; aconcaved metal housing with a flat ange throughout the rim .of thehousing, vSaid flange being bolted to said sheet to electrically connectsaid housing throughout said flange to said ground plate.

6. In combination a chassis of sheet metal adapted to contain electricalequipments, a window of measured size and shape cut through one chassiswall; a sheet of insulating material parallel to and spaced from saidside wall, said sheet having a ground plate adhered to one surface andva :transmission line printed kon the other surface of said sheet, saidground plate having a window in substantial registry with the mentionedwindow in said chassis wall; a metal ring mechanically joining said walland sheet vand surrounding the periphery of said windows, and a cavityhousing overlying the ground plate window with the cavity walls insubstantial alignment with the inner periphery of said ring.

7. In combination defined in claim 6, said transmission line on saidsheet terminating within the boundries ot said windows.

8. In the combination defined in claim 6, said transsion line beingdisposed on said sheet facing said chassis wall vand yelectricallyenclosed by said wall and said ground plate to electively electricallyenclose Asaid line and isolate said line from equipments on the otherside of said sheet.

References Cited in the tile of this patent UNITED STATES PATENTS2,412,249 Brown Dec. `10, 1946 2,751,589 Cary June 19, 1956 FOREIGNPATENTS 1,061,149 France .,a Apr. 8, 1954

